Do yourself a favour and invest in a new radiator.
My previous car, an ED Falcon, was running pretty hot in summer.
I bought a brandnew radiator for $200 from City Dismantlers and the car ran like new !! Seriously, you wouldn't believe the difference !! It saves your engine, trust me.
I was doing 110 km/h uphill and through windy roads, with 4 people in the car and the airco on boost and the engine was
running sweet. BTW, this was in 40+ degrees heat.
I HIGHLY recommend it, and it's heaps easy to install too.